Applied since Middle English to other short metal rods (especially those with knobbed ends). From the notion of an arrow's flight comes the lightning bolt (1530s). A bolt of canvas (c.1400) was so called for its shape. Adverbial phrase bolt upright is from late 14c.

v.

from bolt (n.) in its various senses; from a crossbow arrow's quick flight comes the meaning "to spring, to make a quick start" (early 13c.). Via the notion of runaway horses, this came to mean "to leave suddenly" (early 19c.). Meaning "to gulp down food" is from 1794. The meaning "to secure by means of a bolt" is from 1580s. Related: Bolted; bolting.

bolt

The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.Copyright (C) 2007 by HarperCollins Publishers.Cite This Source

Idioms and Phrases with bolt upright

bolt upright

Precisely perpendicular, erect in carriage, as in She sat bolt upright in her pew. This expression was used in slightly different form by Chaucer in the late 1300s: “She was ... long as a mast and upright as a bolt” (The Miller's Tale).